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Effective Named Entity Recognition for
Idiosyncratic Web Collections
Roman Prokofyev, Gianluca Demartini, Philippe Cudre-Mauroux
eXascale Infolab, University of Fribourg, Switzerland
WWW 2014
April 10, 2014
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Outline
• Introduction
• Problem definition
• Existing approaches and applicability
• Overview
• Candidate Named Entities Selection
• Dataset description
• Features description
• Experimental setup & Evaluation
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Problem Definition
• search engine
• web search engine
• navigational query
• user intent
• information need
• web content
• …
Entity type: scientific concept
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Traditional NER
Types:
• Maximum Entropy (Mallet, NLTK)
• Conditional Random Fields (Stanford NER, Mallet)
Properties:
• Require extensive training
• Usually domain-specific, different collections require
training on their domain
• Very good at detecting such types as Location, Person,
Organization
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Proposed Approach
Our problem is defined as a classification task.
Two-step classification:
• Extract candidate named entities using frequency filtration
algorithm.
• Classify candidate named entities using supervised
classifier.
Candidate selection should allow us to greatly reduce the
number of n-grams to classify, possibly without significant
loss in Recall.
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Pipeline
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Text
extraction
(Apache Tika)
List of
extracted
n-grams
n-gram
Indexing
foreach
Candidat e
Selection
List of
selected
n-grams
Supervised
Classi! er
Ranked
list of
n-grams
Lemmat
ization
n+1 grams
merging
Feature
extractionFeature
extractionFeatures
POS
Tagging
frequency
reweighting

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Candidate Selection: Part I
Consider all bigrams with frequency > k (k=2):
candidate named: 5
entity are: 4
entity candidate: 3
entity in: 18
entity recognition: 12
named entity: 101
of named: 10
that named: 3
the named: 4
candidate named: 5
entity candidate: 3
entity recognition: 12
named entity: 101
NLTK stop word filter
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Candidate Selection: Part II
Trigram frequency is looked up from the n-gram index.
candidate named entity: 5
named entity candidate: 3
named entity recognition: 12
named entity: 101
candidate named: 5
entity candidate: 3
entity recognition: 12
candidate named: 5
entity candidate: 3
entity recognition: 12
named entity: 101
candidate named entity: 5
named entity candidate: 3
named entity recognition: 12
named entity: 81
candidate named: 0
entity candidate: 0
entity recognition: 0
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Candidate Selection: Discussion
Possible to extract n-grams (n>2) with frequency ≤k
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After Candidate Selection
TwiNER: named entity
recognition in targeted
twitter stream
„SIGIR 2012
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Classifier: Overview
Machine Learning algorithm:
Decision Trees from scikit-learn package.
Feature types:
• POS Tags and their derivatives
• External Knowledge Bases (DBLP, DBPedia)
• DBPedia relation graphs
• Syntactic features
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Datasets
Two collections:
• CS Collection (SIGIR 2012 Research Track): 100 papers
• Physics collection: 100 papers randomly selected from
arXiv.org High Energy Physics category
CS Collection Physics Collection
N# Candidate N-grams 21 531 18 129
N# Judged N-grams 15 057 11 421
N# Valid Entities 8 145 5 747
N# Invalid N-grams 6 912 5 674
Available at: github.com/XI-lab/scientific_NER_dataset
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Features: POS Tags, part I
100+ different tag patterns
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Features: POS Tags, part II
Two feature schemes:
• Raw POS tag patterns, each tag is a binary feature
• Regex POS tag patterns:
• First tag match, for example:
• Last tag match:
JJ NNS
JJ NN NN
JJ NN
...
JJ*
NN VB
NN NN VB
JJ NN VB
...
*VB
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Features: External Knowledge Bases
Domain-specific knowledge bases:
• DBLP (Computer Science): contains author-assigned
keywords to the papers
• ScienceWISE: high-quality scientific concepts (mostly for
Physics domain) http://sciencewise.info
We perform exact string matching with these KBs.
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Features: DBPedia, part I
DBPedia pages essentially represent valid entities
But there are a few problems when:
• N-gram is not an entity
• N-gram is not a scientific concept (“Tom Cruise” in IR
paper)
CS Collection Physics Collection
Precision Recall Precision Recall
Exact string matching 0.9045 0.2394 0.7063 0.0155
Matching with redirects 0.8457 0.4229 0.7768 0.5843
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Features: DBPedia, part II
Com ponent siz eCom ponent siz e
NumberofcomponentsNumberofcomponents
0 10 20 30 40 50 60 70
0.4
1
2
4
10
20
40
100
200
400
Com ponent siz eCom ponent siz e
NumberofcomponentsNumberofcomponents
5 10 15 20 25 30 35 40
0.4
1
2
4
10
20
40
100
200
400
Without redirects With redirects
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Features: Syntactic
Set of common syntactic features:
• N-gram length in words
• Whether n-gram is uppercased
• The number of other n-gram given n-gram is part of
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Experiments: Overview
1. Regex POS Patterns vs Normal POS tags
2. Redirects vs Non-redirects
3. Feature importance scores
4. MaxEntropy comparison
All results are obtained using average with 10-fold cross-
validation.
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Experiments: Comparison I
CS Collection Precision Recall F1
score
Accuracy N#
features
Normal POS +
Components
0.8794 0.8058* 0.8409* 0.8429* 54
Regex POS +
Components
0.8475* 0.8524* 0.8499* 0.8448* 9
Normal POS +
Components-Redirects
0.8678* 0.8305* 0.8487* 0.8473 50
Regex POS +
Components-Redirects
0.8406* 0.8769 0.8584 0.8509 7
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The symbol * indicates a statistically significant difference as compared to the
approach in bold.

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Experiments: Comparison II
Physics Collection Precision Recall F1
score
Accuracy N#
features
Normal POS +
Components
0.8253* 0.6567* 0.7311* 0.7567 53
Regex POS +
Components
0.7941* 0.6781 0.7315* 0.7492* 4
Normal POS +
Components-Redirects
0.8339 0.6674* 0.7412 0.7653 50
Regex POS +
Components-Redirects
0.8375 0.6479* 0.7305* 0.7592* 6
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The symbol * indicates a statistically significant difference as compared to the
approach in bold.

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Experiments: Feature Importance
Importance
NN STARTS 0.3091
DBLP 0.1442
Components + DBLP 0.1125
Components 0.0789
VB ENDS 0.0386
NN ENDS 0.0380
JJ STARTS 0.0364
Importance
ScienceWISE 0.2870
Component +
ScienceWISE
0.1948
Wikipedia redirect 0.1104
Components 0.1093
Wikilinks 0.0439
Participation count 0.0370
CS Collection, 7 features Physics Collection, 6 features
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Experiments: MaxEntropy
Precision Recall F1 score
Maximum Entropy 0.6566 0.7196 0.6867
Decision Trees 0.8121 0.8742 0.8420
MaxEnt classifier receives full text as input.
(we used a classifier from NLTK package)
Comparison experiment: 80% of CS Collection as a training
data, 20% as a test dataset.
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Lessons Learned
Classic NER approaches are not good enough for
Idiosyncratic Web Collections
Leveraging the graph of scientific concepts is a key feature
Domain specific KBs and POS patterns work well
Experimental results show up to 85% accuracy over
different scientific collections
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